Original Author(s): Jess Speller Show Original Author(s): Jess Speller This is the first step of synaptic transmission. Some neurotransmitters (eg acetylcholine, ACh) are synthesised in the axon, while others (eg neuropeptides) are made in the cell body.
Once synthesised, neurotransmitters are stored in vesicles within the synaptic terminal until an action potential arrives, causing their release. Neurotransmitters such as acetylcholine are stored within the small synaptic vesicles, whereas neuropeptides reside within large dense-core vesicles. Neurotransmitter ReleaseAction potentials depolarising the synaptic terminal lead to the opening of voltage-gated calcium channels. This allows an influx of calcium in the terminal and fusion of the synaptic vesicles with the cell membrane (exocytosis). Consequently, the neurotransmitter is released into the synaptic cleft. By OpenStax [CC BY 4.0 (https://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons Fig 2 – Diagram showing exocytosis, the process by which neurotransmitters are released into the synaptic cleft. Postsynaptic ReceptorsThe neurotransmitter in the synaptic cleft diffuses across the gap to the post-synaptic membrane. Here, they can bind to two types of post-synaptic receptors.
This can cause either depolarisation to promote or hyperpolarisation to inhibit the action potential generation in the post-synaptic neurone. Inactivation/Removal of NeurotransmittersOnce the post-synaptic membrane has responded the neurotransmitter in the synaptic cleft; it is either inactivated or removed. This can be done in several ways:
Clinical Relevance – Acetylcholinesterase InhibitorsAcetylcholinesterase inhibitors are a class of drug that inhibits the activity of acetylcholinesterase within the synaptic cleft. This increases cholinergic transmission as more acetylcholine is present within the synaptic cleft for longer periods of time. These drugs, such as pyridostigmine, rivastigmine, and donepezil, can be used to treat various conditions:
As cholinergic transmission is widespread throughout the body, particularly mediating the actions of parasympathetic nervous system, these drugs can cause many side effects such as bradycardia, hypotension, diarrhoea, excessive salivation or blurry vision. This website uses cookies. We use cookies to improve your experience on our site and to show you relevant advertising. To find out more, read our privacy policy. What are the steps for transmission at a synapse?The process of synaptic transmission involves four steps:. I. Synthesis and Storage. ... . II. Neurotransmitter Release. ... . III. Neurotransmitter Postsynaptic Receptors. ... . IV. Inactivation of Neurotransmitters. ... . Types of Neurotransmitters.. What are the 5 types of synapses?We can group synapses into 5 types:. Excitatory Ion Channel Synapses. These synapses have neuroreceptors that are sodium channels. ... . Inhibitory Ion Channel Synapses. These synapses have neuroreceptors that are chloride channels. ... . Non Channel Synapses. ... . Neuromuscular Junctions. ... . Electrical Synapses.. |